Learning from Non-Reported Data: Interpreting Missing Body Mass Index Values in Young Children

The objective of this study was to examine the pattern of relations between missing weight and height (BMI) data and a range of demographic, physical activity, sedentary behavior, and academic measures in a young sample of elementary school children. A secondary analysis of a large cross-sectional study, PLAY-On, was conducted using self-reported data from a convenience sample of fifth- to eighth-grade students (9–14 years) attending 30 elementary schools in Ontario, Canada. Items assessed related to demographics (age, gender, and ethnicity), physical activity (energy expenditure, location, and sport participation), sedentary behavior (communication and screen-time), and academics. Of the 2,111 children who were included in the analyses, 960 (45.5%) were missing BMI data. Children without BMI data were more likely to be younger, female, of non-white ethnicity, have lower daily energy expenditure values, not participate in school sports, and have lower-rated academic standing than those children with BMI data. Overall, this study demonstrates characteristics of children who fail to self-report their height or weight. The trend for younger children to be more likely to fail to report BMI suggests that some children may be unmotivated non-responders. Meanwhile, the trend for girls to be more likely to fail to report weight than boys indicates that some girls may be motivated non-responders. Self-report BMI might include too much missing data to be effective for determining children's progress toward previously established targets for intervention and surveillance efforts.